The present invention relates to use of a psychophysical method and apparatus for entoptically evaluating and mapping the human foveal area vasculature with respect to the retinal point of fixation (RPF). Knowing the location of the RPF is essential in modern ophthalmic surgery because it can be inadvertently damaged during photocoagulation, resulting in marked vision loss. Unfortunately, the RPF is not visible on direct examination of the eye; its location must be determined subjectively and then related to observable landmarks. The present invention uses well-known techniques of entoptic visualization in a novel way to accomplish this goal.
While entoptic (referring to visual phenomena having their seat within the eye) observations of retinal vessel shadows were recorded more than 100 years ago, these subjective sensations have thus far found limited use in modern medical practice. In part, this is because convenient objective photographic methods have been developed for studying the retinal vasculature, thus relegating subjective observations (with their lack of objective controls) to a secondary role. In practice, for example, entoptic perceptions of the geometric patterns of blood vessels have been described only schematically, while fluorescein angiography has produced a wealth of detailed photographs. But what is lacking in the photographs (and other direct observations) as well as the entoptic perceptions to date is quantification of the location of the RPF with respect to the vasculature architectures.
Instead of the RPF, what is evident on most retinas (and what is usually assumed to be concentric with the RPF) is the foveal avascular zone (FAZ), an area surrounding the fovea where retinal vessels are absent or decreased. Recent research has shown that the FAZ and the RPF are not, as previously assumed, always concentric. The assumption has persisted because it is approximately correct in most people and, prior to the present invention, there was no convenient way to check it in a given patient. Now that a simple, accurate mapping system has been developed and tested, there are data to suggest that therapeutic failures following photocoagulation (defined as loss of 6 or more lines of visual acuity) may be reduced up to 20% in specific groups of patients having preoperative mapping of the retinal vasculature with respect to the RPF.